1. Field of the Invention
The present invention relates to a method of air conditioning in vehicles and in aircraft in particular in accordance with the introductory clauses of Patent Claims 1, 2 or 5, or to a device in accordance with the introductory clause of Patent Claim 18.
2. Prior Art
It is common in motor vehicles to mix circulated air, i. e. air from the interior of the vehicle, and supplied or outside air to produce the air flow serving to condition the air inside the vehicle. Depending on the temperature, the supplied or outside air must be heated or cooled or can be used directly to cool the passenger compartment.
In commercially available air conditioning installations for motorcars the circulated air is admixed to the outside air almost exclusively in consideration of exhaust gas aspects: when the motorcar stops at a traffic light or in a traffic jam the system is automatically or manually switched over from outside air supply to circulated-air mode.
From the German Patent DE 195 40 566 A1 it is known to admix dry circulated air to humid outside air in order to avoid that the windows of the motorcar will be clouded by the moisture carried in the outside air.
In busses, trains or aircraft the admixture of circulated air to the outside air is not employed to the same extent as this is the case in motorcars; the reason might reside in the fact that bacteria, germs, odours, sweat etc. should not be distributed by the circulated air via the air conditioning system all over the passenger cabin. Exemplary reference is made to the German Patent DE 39 26 638 A1 which reflects prior art in air conditioning systems for busses.
Moreover, for an explanation of all the particulars which are not described here in further details explanation is made to both the above-quoted prior art documents and the prior art publications which will also be identified in the following.
In aircraft the following additional problem arises: the supplied air is not only very cold but also very dry.
When circulated air is admixed to the outside airxe2x80x94as in prior artxe2x80x94exclusively in consideration of energy aspectsxe2x80x94which occurs, as a rule, for cooling the passenger cabin in aircraft, which is xe2x80x9cheatedxe2x80x9d by the passengersxe2x80x94events occur which include the following problems:
In the case of strong solar radiation prior art simply provides for passenger cabin cooling in a way that large quantities of very cold outside air are admixed to the air flow supplied to the passenger cabin; the consequence is a very dry cabin air, which the passengers normally perceive as uncomfortable even though they frequently accept it. The dry air may even cause trouble in the respiratory system of sensitive persons.
In the case of weak solar radiation, by contrast, the fraction of circulated air in the air flow supplied to the passenger cabin is very high in order to save heating energy. As has been found by the inventors, the CO2 level in the cabin air is hence very high in conventional aircraft air conditioning installations, frequently ranging above an agreeable or tolerable limit which is characterised by the so-called Pettenkofer threshold.
Furthermore, for reasons which are only speculative despite the foregoing statements, some airline companies dispense with the admixture of circulated air for air conditioning inside an aircraft.
As, however, the outside air and hence the supplied air is very cold, as has been outlined above, the admixture of warm circulated air and cold supplied air would present the advantage that, compared against the use of supplied air alone, the quantity of energy is reduced which is required for achieving a moderate temperature of the air flow supplied to the passenger cabin.
The present invention is based on the problem of providing a method of as well as a device for air conditioning in vehicles and in aircraft in particular, which will permit the achievement of a moderate temperature in the passenger cabin, which is agreeable particularly from the viewpoints of comfortableness and tolerability, at the lowest energy consumption possible.
Inventive solutions to this problem are defined in the parallel Patent Claims 1, 2 or 5, respectively; the features defined in these claims are also suitable for cumulative application. Improvements of the invention are the subject matters of the dependent claims.
Devices for realising the inventive methods are the subject matters of the Claims 16 et seq.
The different inventive solutions characterised in the claims are based on the common inventive idea that the admixture of the outside air and the circulated air should be made in consideration of viewpoints of comfortableness or tolerability, respectively, rather than in consideration of energy or exhaust gas aspects.
In the solution defined in Claim 1 the fraction of the circulated air in the supplied air flow is limited by means of at least one CO2 sensor such that the CO2 fraction in the air in the passenger cabin will not exceed a defined threshold. The CO2 fraction threshold amounts to 0.15% by volume and preferably to 0.10% by volume, for instance; this value corresponds to the so-called Pettenkofer threshold above which signs of fatigue and/or irritations of the eyes or the respiratory tract may occur.
The control or regulation of the circulated-air fraction in a way that a defined carbon dioxide level will not be exceeded constitutes hence a xe2x80x9cmasterxe2x80x9d controller for all further or subordinate systems controlling the fraction of the circulated air, which are preferably xe2x80x9cslavexe2x80x9d control systems in dependence on the xe2x80x9cmasterxe2x80x9d controller.
In this respect it is particularly preferable (even though not definitely necessary) that the inventive device be so designed that it supplies an outside air quantity of 0.5 m3/min per passenger at minimum into the passenger cabin. It is moreover preferred that the air supply system should be so designed that it ensures 20 air exchange cycles at minimum per hour.
The inventive method and the inventive device are suitable for application in vehicles of any kind such as motorcars, lorries, busses or ships. The method or the device, respectively, according to the present invention are particularly preferred, however, in aircraft where on account of the very cold outside air, which is present at altitudes at which passenger air planes normally cruise, the problem occurs that the supplied outside air is very dry after it had been heated to room temperature. Moreover, air planes are equipped with a pressurised cabin so that due to the largely closed systemxe2x80x94with a leakage rate typically amounting to 10% in aircraft equipped with a pressurised cabinxe2x80x94farther-going problems arise in addition to those occurring in other vehicles, specifically in consideration of tolerability aspects.
In aircraftxe2x80x94and, of course, also in other vehiclesxe2x80x94it is therefore preferred that below the threshold predetermined for the circulated air quantity by the CO2 sensor the fraction of the circulated air in the supplied air flow be controlled in such a way that the relative humidity will be maintained within an xe2x80x9cagreeablexe2x80x9d humidity range which is higher than the relative humidity in the supplied outside air after heating to room temperature. In distinction from prior art in motor vehicles, where the fraction of circulated air in the circulated air quantity is adjusted exclusively in consideration of energy balance or exhaust gas aspects while in any other respect the humidity is rather considered to be disturbing, the fraction of circulated air in the air volume circulated in the vehicle in accordance with the inventive method is so controlled or adjusted, respectively, that the relative humidity is approximately maintained within a predetermined (agreeable) range.
Compared against conventional methods, the inventive method entails the particular advantage that there is no necessity to humidify the supplied air or that it a substantial reduction of the water quantity is possible, which must be added to the supplied air for humidification.
It is hence possible without any problems, in particular, to bring the relative humidity to a level of at least 20%, preferably to a value of more than 30%, at cabin temperature and particularly at 23xc2x0 C. With these values an agreeable room climate is achieved.
In order to avoid that as a consequence of the comparatively high percentage of circulated air bacteria, germs, odours, sweat etc. will be distributed within the passenger cabin the supplied air flow is introduced via at least one filter into the passenger cabin. The air supply may take place via the vehicle cover and/or the rear side of the front seats in a manner known per se. With this concept it is possible in particular to provide the air outlets in the rear side of the backrest of the respective front seat, inclusive of possibly disposed foldable tables, etc.
The filter or filters may be large-area filters with a low flow resistance in particular which purify the air preferably in view of bacteria, odours and aerosols. The term xe2x80x9caerosolxe2x80x9d is to be understood in this context to encompass particles, organic substances, dusts, endotoxins, droplets, etc.
The large-area filter or filters with a low flow resistance, which is or are provided, for instance, in the cabin top wall or in the respective front seat, may be micro filters or composite filters, in particular. In an improvement of the invention the filter or filters is/are a micro filter coated with activated carbon or with a cartridge filled with activated carbon and/or a micro filter with an additional zeolith filter. Moreover, the filter or filters may be electrically biased and/or non-woven fibre materials.
On account of the large-area filter or filters, the circulated air can yet be supplied at a low air flow rate, with controlling means being possibly associated with each vehicle seat, which may comprise a room climate measuring unit if necessary. Room climate measuring units are described, for instance, in the German Patent DE 32 05 704 A1 or in the article xe2x80x9cDevelopment of a measuring unit for determining the physical room climate conditionsxe2x80x9d as published in the journal xe2x80x9cGesundheits-Ingenieurxe2x80x9d [The Health Engineer], 1985, pages 175 to 192xe2x80x9d. Moreover, explicit reference is made to these prior art documents for an explanation of all particulars which are not described here in more details.
Due to the use of room climate measuring units it is possible to control the surface temperature of the air discharge surface and the motion of the air in physiologic terms and particularly in consideration of the thermal comfortableness. Hence every occupant or passenger can adjust the air flow to which he or she is exposed in correspondence with his or her personal requirements.
It is possible in particular to provide the filter or filters in the discharge opening of the air flow in the passenger cabin; according to an alternative or additionally at least one part of the air flow may be discharged through discharge nozzles.
The inventive device suitable for carrying through the method comprises at least one CO2 sensor and/or a humidity sensor in the exhaust air. The output signals of the sensor or sensors, respectively, are applied to a controller, which controls the percentage of circulated air in the circulated air quantity. The controller can hence adjust the percentage in such a way that the desired relative humidity will be reached or that the CO2 threshold will not be exceeded.
It is, of course, possible to provide a further humidity sensor, which detects the humidity in the supplied air flow (which is dry, as a rule, in aircraft) so that variations of the relative humidity as a consequence of humidity variations in the supplied air will be avoided.
The recovery of the water carried in the air in the passenger cabin can be alternatively or additionally realised by the provision that the humidity contained in the discharged airxe2x80x94i.e. the cabin air discharged, for instance, in an air plane for pressure equalisation to the outside due to the supplied outside airxe2x80x94is condensed and returned into the air flow supplied into the passenger cabin.
With the inventive provisions it is normally no longer necessary to carry water on board for humidification of the air in the passenger cabin.